Simulation of buoyancy-driven instability during CO2 absorption in aqueous reactive solution

This work deals with the mathematical modelling of the CO2 absorption in initially quiescent aqueous solutions, coupled with a chemical reaction in the liquid phase, inside a Hele-Shaw cell. Two different aqueous solutions are considered experimentally and it is observed that the absorption, initially driven by the diffusion, leads to the appearance of gravitational instabilities with different dynamics, depending on the considered case. Assuming that these instabilities are triggered by a Rayleigh-Taylor mechanism, a two-dimensional model, coupling the diffusion, the chemical reaction and buoyancy-driven convection, is proposed to simulate the development of such instabilities. It is observed that the simulations reproduce the density variation pattern and that the simulated instability dynamics agree qualitatively with the experimental observation in both cases considered. In addition, the simulation enables to assess the influence of the instabilities on the CO2 absorption rate and it is observed that, depending on the considered aqueous solution, the pattern of density variation drives the instability dynamics and therefore influences the mass absorption rate after the instability. Especially, for one of the considered cases, the particular pattern of the density variation leads to an instability pattern which does not enhance the mass absorption rate.